San Mateo's winters are mild, with temperatures ranging from near-freezing in January and December to moderate highs around 20-21°C. Spring brings steady warming, with temperatures gradually increasing by about 1-2°C each month from March to June, peaking at an average of 19°C in July and August. Summer is warm but not hot, with temperatures rarely exceeding 41°C. Autumn sees a decline in temperature, returning to winter-like conditions by December. Overall, the city experiences mild climate throughout the year, with minimal extreme temperature fluctuations.